How to change which resolution Arkenfox spoofs to?

I started using Arkenfox's user.js on FireFox, but later when I ran a test on Cover Your Tracks the detected screen size was 1300x600 which is not at all a common screen resolution. The test also says "One in 285 people has this value". Weirdly enough, when I used the CanvasBlocker addon which spoofed(?) the screen resolution to the original -which is more common- by default, the results went from "Your browser has a nearly-unique fingerprint" to "Your browser has …

change privacy resolution